The existence of slimes, bacteria and fungi in waters, particularly industrial waters, is an ongoing problem. Examples of industrial waters where slimes and the like can interfere with industrial processes include cooling towers, effluent discharges, waters used for conveying particulate matter, and the like. In particular, pulp and paper mill production waters are affected by resident microflora and the slimes produced by the microflora. These slimes can interfere with the production process, causing nozzle plugging, screen blinding, and sheet defects such as holes and discolorations.
The term slime or slimes refers to a broad range of mucous, viscous, and leathery materials. These materials typically comprise or originate from polymeric, generally polysaccharide excretions produced by a broad spectrum of microorganisms.
Typically, biological deposits of all types including slimes are treated by the addition of biocides or chemicals. Where slimes are present, biocides are frequently added in an effort to destroy the bacteria or microflora population which may produce the slimes. Chemicals which have been used for this purpose include chlorine compounds including the chlorophenates; organomercurial compounds such as phenylmercuric acids; thiocarbamate compounds; thiocyanate compounds such as the isothiocyanates and methylene-bis-thiocyanate; tributyltin oxide; and the like. However, these chemicals tend to be costly and highly toxic in the quantities known to be required for effective control of microbial populations. As a further drawback, most of these chemicals tend to be most effective at an acid pH, such that in more alkaline systems, even greater concentrations are required. Additionally, it appears that no precise correlation exists between the size of the bacterial population and the accumulation of slime. Substantial slime accumulations have been observed even in waters having a low bacterial count. Similarly, high bacterial counts have been observed in waters having no significant slime accumulation. Consequently, use of a biocide may not adequately control biological slime accumulations.
As an alternative to treatment with biocides, it is also known that slime accumulation can be controlled to a certain degree by use of the enzyme levan hydrolase, also known as levanase. It was discovered that levan, a polysaccharide produced by a variety of bacteria, is a significant component of many industrial slimes. U.S. Pat. No. 3,824,184 to Herbert J. Hatcher, discloses the addition of levan hydrolase to industrial waters having a slime accumulation or potential slime problem. The enzyme can hydrolyze the levan present in the slimes, substantially decomposing the slimes and lessening the problems associated with their presence in the water systems. However, the enzyme does nothing to limit or reduce the microbial population.
We have discovered that the combination of a biocide and a polysaccharide degrading enzyme will significantly reduce microbial counts and slime accumulations, far more effectively than a biocide or an enzyme alone.